1. Field of the Invention
The present invention pertains to a method of producing a piezoelectric device used in ink jet recording heads, etc., and in particular, to a method of producing a piezoelectric device, etc., by means of which crystallization of the entire layer-built structure can be performed all at once and productivity thereby raised, and its products.
2. Description of the Related Art
Piezoelectric devices are elements with electric equipment conversion capability and are made by sandwiching a piezoelectric ceramic such as crystalline lead zirconate titanate (PZT), etc., between electrodes. In order to produce this piezoelectric device, a diaphragm layer, bottom electrode layer, piezoelectric thin film layer, and a top electrode layer are formed in succession on a substrate. In conventional methods of producing piezoelectric devices, a different method is used to produce each layer because the composition of each layer is different. For instance, the diaphragm if formed by the thermal oxidation method, while the electrode layers are formed by sputtering, etc. Moreover, the so-called sol-gel method is used to produce the piezoelectric thin film layer. By means of the sol-gel method, a sol, or the organic metal precursor, is applied, the sol is dried and pyrolyzed, and finally, the product is heat treated at a high speed and thereby crystallized.
Methods of producing thin films in general are further discussed in, for instance, Phillips J. Res. 47(""93), pp. 263-285, etc.
Nevertheless, by means of conventional methods of producing piezoelectric devices, the thin film of one layer is completed and then the film of the next layer is formed and therefore, there is a problem in that the structure of each layer is completely crystallized and adhesion between the layers is weak. When adhesion between the layers is poor, peeling occurs during the production process, leading to poor yield, and peeling occurs during use, resulting in poor reliability. Therefore, there is a demand for a method of production that results in strong adhesion.
Moreover, since each layer is as it is being crystallized, there are inevitably many processes needed to complete the piezoelectric structure. Because there are many processes, there is naturally an increase in the production cost. Therefore, there is a demand for a production method with few processes.
Thereupon, a method whereby a piezoelectric device of a piezoelectric ceramic that has been applied to a substrate and pyrolyzed is placed in a specific alkali solution and crystallized is recorded in xe2x80x9cApplication of Hydrothermal Mechanism for Tailor-Making Perovskite Titanate Films,xe2x80x9d IEEE Proc. of the 9th Int""l Symp. on Electrets, Shanghai, China, September 25-30, pp. 617-622 (1996), W-ping Xu, Masanori Okuyama, et al. This method of crystallization in an alkali solution is called the hydrothermal method. When compared to the sol-gel method crystallization at a relatively low temperature is possible by means of this hydrothermal method and therefore, there are a number of advantages to this method. The inventors of the present invention hit upon the idea that a piezoelectric device with a multi-layered structure could be crystallized all at once by using this hydrothermal method and successfully completed experiments with this production method confirming this point.
In light of the aforementioned facts, a first objective of the present invention is to present a functional thin film with high adhesion between layers and high reliability, a piezoelectric device, an ink jet recording head and a printer.
A second objective problem of the present invention is to present a method of producing a piezoelectric device and a method of producing an ink jet recording head, both of which have fewer production processes than conventional production methods and therefore have a lower production cost.
The invention that solves the aforementioned first objective is a functional thin film, characterized in that a mixed layer where the components of thin film layers made of different components are mixed together is formed between the respective thin film layers. This film is not only xe2x80x9cfunctional thin film,xe2x80x9d but also film that is used for any purpose for which many thin films are used. There is a region of a specific thickness where the components of two layers are mixed at the interface between the respective layers of the thin film structure.
Another invention that solves the aforementioned first objective is a piezoelectric device, characterized in that it comprises at least one (1) piezoelectric thin film layer and two (2) electrode layers, and a mixed layer that is a mixture of the components of adjacent layers is formed between the respective layers. The crystals of the two layers are intricately intertwined in the mixed layer and therefore, adhesion between the layers is high.
Still another invention that solves the aforementioned first objective is a piezoelectric device that further comprises at least one (1) diaphragm layer, with a mixed layer that is a mixture of the components of the aforementioned diaphragm layer and the adjacent electrode layer formed in between the respective layers.
Thickness of the aforementioned mixed layers is, for instance, 5 nm or thicker. By means of conventional production methods, thickness of the part where the compositions are mixed was less than 3 nm and therefore, adhesion between layers is improved by the presence of this thick mixed layer.
For instance, the metal alkoxide that comprises the piezoelectric thin film layers is any piezoelectric ceramic selected from lead zirconate titanate (Pb(Zr, Ti)O3: PZT), lead lanthanum titanate ((Pb, La)TiO3), lead lanthanum zirconate ((Pb, La)ZrO3), lead lanthanum zirconate titanate ((Pb, La)(Zr, Ti)O3: PLZT), or lead magnesium niobate zirconate titanate (Pb(Mg, Nb)(Zr, Ti)O3: PMN-PZT).
For instance, the piezoelectric device of the present invention has two (2) or more piezoelectric thin film layers and three (3) or more electrode layers and is made by sandwiching at least one of the piezoelectric thin films between electrode layers. This type of structure is generally called a bimorph.
Still another invention that solves the aforementioned first objective is an ink jet recording head with the piezoelectric device of the present invention as the piezoelectric actuator. For instance, it has
a) a pressure chamber structure that forms the pressure chamber,
b) a diaphragm on one side of the pressure chamber, and
c) a piezoelectric device that is placed facing the diaphragm in the pressure chamber and is made so that it deforms the aforementioned diaphragm.
Another invention of the present application that solves the aforementioned first objective is a printer that has the ink jet recording head of the present invention as a printing means. For instance, it has
a) a recording medium conveyor that is made so that it is possible to feed in and carry out the recording medium and
b) a head control circuit by means of which the ink jet recording head prints at any desired position of the recording medium that has been fed by the recording medium conveyor.
Still another invention that solves the aforementioned second objective is a method of producing a piezoelectric device with at least one (1) piezoelectric thin film layer and at least two (2) electrode layers, characterized in that it comprises
a) the process whereby amorphous piezoelectric thin film layers, which are the amorphous state of each of the piezoelectric thin film layers, are formed,
b) the process whereby amorphous electrode layers, which are the amorphous state of each of the electrode layers, are formed, and
c) the process whereby after each amorphous piezoelectric thin film layer and each amorphous electrode layer have been laminated, hydrothermal synthesis is performed to crystallize the amorphous piezoelectric thin film layers and the amorphous electrode layers.
Moreover, another invention that solves the abovementoned second objective is a method of producing a piezoelectric device that further comprises at least one diaphragm. This method further comprises the process whereby an amorphous diaphragm, which is the amorphous state of the diaphragm layer, is formed and whereby once the amorphous diaphragm layer, as well as each of the amorphous piezoelectric thin film layers and each of the amorphous electrode layers, have been laminated, the aforementioned amorphous diaphragm, amorphous piezoelectric thin film layers, and amorphous electrode layers are crystallized by hydrothermal synthesis in the process of hydrothermal synthesis.
For instance, the aforementioned process of forming the amorphous piezoelectric thin film layer comprises the process whereby precursor made from an organic metal solution is applied by the sol-gel method, the MOD (metal-organic deposition) method, or the coprecipitation method and the process whereby said precursor is dried and pyrolyzed.
For example, by means of the process whereby the aforementioned precursor is dried and pyrolyzed, the precursor is dried at 150xc2x0 C. to 200xc2x0 C. and the dried precursor is pyrolyzed at 300xc2x0 C. to 500xc2x0 C.
By means of the aforementioned hydrothermal synthesis process, for instance, the pyrolyzed precursor is immersed in a specific alkaline solution and crystallization is promoted under specific conditions.
The aforementioned alkaline solution here comprises any of KOH, Ba(OH)2, Ba(OH)2+Pb(OH)2 or KOH+Pb(OH)2.
The aforementioned specific conditions of the hydrothermal process are for instance, a temperature of 100xc2x0 C. to 200xc2x0 C. and pressure of 10 atmospheres or less.
By means of the present invention, a structure is made whereby amorphous piezoelectric thin film layers are sandwiched by amorphous electrode layers by repeating the process whereby the aforementioned piezoelectric thin film layers are formed at least two (2) times or more and repeating the process whereby the aforementioned amorphous electrode layers are formed at least three (3) times or more.
Moreover, yet another invention that solves the aforementioned second problem is a method of producing an ink jet recording head comprising the piezoelectric device made by the production method of the present invention, and is a method of producing an ink jet recording head comprising
a) the process whereby a diaphragm is formed on one surface of a substrate,
b) the process whereby a piezoelectric device is made on the diaphragm, and
c) the process whereby the substrate is etched and a pressure chamber is formed so that the diaphragm with the piezoelectric device will form one side of the pressure chamber.